Heat pump type hot-water supply equipment is equipped with, in general, a tank unit 71 having a hot-water reservoir tank 70, and a heat-source unit 73 having a refrigerant circuit 72, as shown in FIG. 7. The refrigerant circuit 72 is so configured as to connect a compressor 74, a hydrothermal exchanger 75, an expansion valve 77, and an evaporator 78 in order. The tank unit 71 includes the hot-water reservoir tank 70 and a circulation path 79. The circulation path 79 is provided with a pump 80 for water circulation and a heat exchange path 81 which constitutes a part of the hydrothermal exchanger 75.
Here, the operation of the aforementioned heat pump type hot-water supply equipment will be described.
First, the compressor 74 is driven while the pump 80 for water circulation is also driven (operated). Then, stored water (hot water) flows out from the water intake provided at the bottom of the hot-water reservoir tank 70 to the circulation path 79, and the hot-water flown out flows through the heat exchange path 81. Here, the hot water flowing through the heat exchange path 81 is heated (boiled) by the hydrothermal exchanger 75. The hot water heated flows into the top portion of the hot-water reservoir tank 70 from the hot-water inlet. Thereby, the hot water of high temperature is stored in the hot-water reservoir tank 70.
Conventionally, as a refrigerant circulating the refrigerant circuit, such a refrigerant as dichlorodifluoromethane (R-12) or chlorodifluoromethane (R-22) was used. However, from the point of preventing destruction of the ozone layer, preventing environmental pollution, and the like, an alternative refrigerant such as 1,1,1,2-tetrafluoro ethane (R-134a) has been used as a refrigerant. Still, the alternative refrigerant such as R-134a has a problem of having a high ability to cause a greenhouse effect or the like. Therefore, it has been gradually recommended in recent years to use a natural system refrigerant, which is free of the aforementioned defect, as a refrigerant. As a natural system refrigerant of this kind, carbon dioxide, for example, is well known.
As the outside air temperature varies along with the season's transition, a load change occurs in the aforementioned equipment. According to the load change, the refrigerant cycles also change. This means that the preferable amount of circulated refrigerant is different for every season. Thus, it has been difficult to operate with the optimum amount of circulated refrigerant unless some measures are taken. If the actual amount of the circulated refrigerant is less than the optimum amount of the circulated refrigerant, the superheated refrigerant is sucked into the compressor 74, causing the compressor 74 to be operated in the excessively superheated condition. In contrast, if the actual amount of the circulated refrigerant exceeds the optimum amount of the circulated refrigerant, the refrigerant, which has not been evaporated completely, is sucked into the compressor 74, causing the compressor 74 to be operated in the wet condition. As a result, the reliability of the compressor 74 is degraded.
The present invention is developed to solve the aforementioned conventional problems. The object of the present invention is to provide a technique which enables to operate with a proper amount of circulated refrigerant by controlling the amount, and prevents an excessive superheat operation or a wet operation.